Apparatus for measuring oxygen content of a fluid

ABSTRACT

Apparatus for measuring oxygen content of fluids at elevated temperatures includes a sensor or probe which comprises a Cr2O3 tube and a solid electrolyte button sealing that end of the tube that contacts the fluid. A solid oxygen reference material in the tube made of chromium or a chromium alloy contacts the button and the other end of the tube is sealed with a molybdenum cap. A thermocouple and a lead wire pass through the cap into the tube. A quartz tube surrounds the Cr2O3 tube and button with its outer end in sealing engagement with the button. An electronic conductor has one end extending into the fluid. In one embodiment the conductor is a tube surrounding the quartz tube and in another it is a separate rod or tube. In both embodiments the conductor is preferably a mixture of Al2O3 and molybdenum. The lead wire and the other end of the conductor are connected to a voltage measuring means.

United States Patent Rittiger et al.

[ June 6, 1972 1541 APPARATUS FOR MEASURING OXYGEN CONTENT OF A FLUID[72] inventors: Robert S. Rittiger, Allegheny Township; Charles K.Russell, Franklin Township,

21 A 1. No.1 115,509

G. R. Fitterer,J. Metals, 18, 961 (1966). G. R. Fitterer, J. Metals, i9,92, 1967).

G. R. Fitterer, J. Metals, 20, 27, i967). Thoma C. Wilder, Trans. of theMetallurgical Society of Aime, Vol. 236, pp. i035- 1040, July 1966.

Primary Examiner-G. L. Kaplan Attorney-Martin J. Carroll [57] ABSTRACTApparatus for measuring oxygen content of fluids at elevatedtemperatures includes a sensor or probe which comprises a Cr,0 tube anda solid electrolyte button sealing that end of the tube that contactsthe fluid. A solid oxygen reference material in the tube made ofchromium or a chromium alloy contacts the button and the other end ofthe tube is sealed with a molybdenum cap. A thermocouple and a lead wirepass through the cap into the tube. A quartz tube surrounds the Cr,0,tube and button with its outer end in sealing engagement with thebutton. An electronic conductor has one end extending into the fluid. Inone embodiment the conductor is a tube surrounding the quartz tube andin another it is a separate rod or tube. In both embodiments theconductor is preferably a mixture of Al,0, and molybdenum. The lead wireand the other end of the conductor are connected to a voltage measuringmeans.

12 Claims, 2 Drawing APPARATUS FOR MEASURING OXYGEN CONTENT OF A FLUIDThis invention relates to apparatus for measuring the oxygen contentand/or activity of fluids at elevated temperatures, and moreparticularly, to apparatus that rapidly deter mines the oxygen contentof liquid steel in a furnace or container without removing a sample.Since our invention, at present, is most useful and most needed for thispurpose, this use will be stressed hereinafter. However, our inventionis also applicable for determining oxygen in other fluids attemperatures above approximately 700 C., such as oxygen in liquid copperor hot furnace gases. v

Apparatus suitable for this purpose "is disclosed in the copendingapplication of Fruehan and 'Turkdogan, Ser. No. 39,530, Filed May Ill,1970. However, the apparatus disclosed therein is basically laboratoryapparatus and is not suitable for use in large steelmaking furnaces andcontainers because of cost, fragility, reliability when used byrelatively unskilled workmen, ease of use and other factors important inadapting the basic cell concept to industrial use.

Other apparatus suitable for commercial work is disclosed in ourco-pending application Ser. No. 54,986, Filed July 15, 1970. Theapparatus shown therein is inexpensive, but can only be used once. It issometimes desirable to have such apparatus that can be re-used eventhough it is more expensive and it is for this purpose that the presentprobe was developed.

It is therefore an object of our invention to provide apparatus formeasuring oxygen content and temperature in substantially the sametheoretical manner as that of our prior application, but which can bere-used.

This and other objects will be more apparent afier referring to thefollowing specification and attached drawings, in which:

FIG. 1 is a sectional view of one embodiment of our invention; and

FIG. 2 is an elevation, with parts broken away, and shown in section ofanother embodiment of our invention.

Referring more particularly to FIG. 1, reference numeral 2 indicates ametallic oxide tube having its lower or outer end sealed by anelectrolyte button 4 made of ZrO, containing 3 to 10% CaO and its upperor inner end sealed by a molybdenum cap 6. For best operation the sizeof the button is kept as small as possible. An oxygen referencematerial8 is located within tube 2 in contact with button 4. Thereference material 8 must be liquid or solid at the operatingtemperature and is preferably chromium or a chromium alloy such as aNi-Cr alloy. However, Mo, Ta, or an alloy thereof may be used. The tube2 must be an oxide of the reference metal, must not melt at thetemperature of use, and must act as an electronic conductor at thattemperature. The-tube is preferably made of 0: 0,. A thermocouple 10passes through cap 6 with its lower end extending into tube 2. Thethermocouple 10 may be of a standard straight type with its two wirespassing through a 2- hole refractory insulator, but is preferably astandard U-tube type in which one wire is secured in each leg of theU-tube and connected at the center of the tube. One such thermocouple isshown in Mead US. Pat. No. 2,999,121 dated Sept. 5, 1961, or 3,298,874dated Jan. l7, 1967. A refractory insulated molybdenum wire 12 passesthroughcap 6 into tube 2 and is held in place by set screw 14. A quartztube 16 surrounds tube 2 with its lower end in sealing engagement withbutton 4 which does not extend beyond the end of the tube 16. The tube16 includes an outwardly extending radial flange 16F at its upper end.For best operation a slight clearance such as l mm. should be providedbetween tubes 2 and 16 to prevent cracking of tube 16 due to thermalexpansion. A cermet tube 18 closely surrounds the tube 16 and has itsbottom tapered inwardly with an opening therein for exposure of thebutton 4 to the fluid F being analyzed. The tube 18 has an outwardlyextending radial flange 18F at its upper end which abuts flange 16F. Thetube 18 must be made of a material which is an electronic conductor andwill not melt at the temperature of use. its metallic phase should bethe same as that of cap 6 and wire 12 since otherwise a thermoelectriccorrection must be made to the electrolytic cell reading. It ispreferred to use a mixture of A1 0 and molybdenum. An internallythreaded sleeve 20 surrounds flanges 16F and 18F and has a bottom flange20F which bears against flange 18F. A cap 22 has a threaded reduceddiameter section 24 which is threaded into sleeve 20 to hold the partsassembled. The cap 22 has a hole 26 therethrough for passage of theinsulated thermocouple wires and wire 12. A wire 28, preferably made ofmolybdenum, is attached to cap 22 by means of a screw 30. The sleeve 20and cap 22 must be electrically conductive and are preferably fabricatedfrom the same metal as the metal phase of the cermet tube 18, but ifthese parts are at a reasonably uniform temperature in use, nosignificant thenno-electric error is created if the parts are made ofstainless steel. The thermocouple wires and wires 12 and 28 areconnected to a potentiometer 32. If the assembled unit is to be placedin a metal bath F with a portion of the cermet tube 18 exposed to slagor to air, a refractory oxide sleeve 34 of a material resistant to slagattack and oxidation is preferably placed over that portion of tube 18so exposed. Sleeves made of aluminum oxide or magnesium oxide areexamples of such protective refractory materials, but this does notexclude other refractory oxides or combinations thereof. In addition, ifthe sensor is to penetrate a slag layer during immersion, a metal cap 36is placed over the end of the sensor to protect the electrolyte. Thiscap must be made of a material which will melt upon contacting themolten metal. In measuring the oxygen content of steel, a steelprotective cap is usually employed. To provide a snug fit between button4 and quartz tube 16 the quartz tube 16 may be heated so that it flowsaround the electrolyte button 4. Another method is to precision grindthe electrolyte button 4 so that it just fits inside the quartz tube 16.ln either case, the end of the tube 16 should not extend beyond theelectrolyte button and should be ground off, if necessary.

In operation, the sensor can either be partially immersed (about onehalf of its length) from above the metal bath or installed in the sidewall or bottom of a refractory container such as a steel ladle. Themolten metal F containing an unknown amount of dissolved oxygen contentcontacts the exposed end of the zirconia button 4 and also the exposedend of cermet tube 18 which is an electrical conductor. Thus, anelectrical connection is made from button 4 through tube 18, sleeve 20,cap 22 and lead 28 to potentiometer 32. An electrical connection is alsomade from button 4, through the reference alloy 8, oxide tube 2, cap 6and wire 12 to the other terminal of potentiometer 32. The enif that isread, in combination with the temperature, can be mathematicallyconverted to oxygen content by the general formulas shown in the Fruehanet al. application.

In the embodiment of FIG. 2 a separate rod 40 is used in place of tube18 and is made of the same material as that tube. One end of the rod 40is inserted in the fluid F and the other end connected by means of lead42 to potentiometer 32. Those parts of probe 44 within quartz tube 16'are the same as in the first embodiment of the invention and areindicated by the same reference numerals. Tube 16 differs from tube 16by the omission of flange 16F. A protective alumina tube 46 surroundsthe tube 16' and is cemented thereto by refractory cement. The tube 46has a radial flange 46F at its inner end. A protective metal cap 36' maybe provided over the lower end of tube 16' for the same reason as cap 36in H6. 1. This embodiment is less expensive than the first embodimentbecause the cost of the rod 40 is substantially less than the cost oftube 18. The operation of this embodiment is essentially the same asthat of the first embodiment.

While two embodiments of our invention have been shown and described, itwill be apparent that other adaptations and modifications may be madewithout departing from the scope of the following claims.

I We claim:

1. Apparatus for measuring the oxygen content of a fluid comprising afirst tube, an electrolyte button sealing the outer end of said firsttube and adapted to contact said fluid, a metallic oxygen referencematerial within said first tube in contact with said button, saidreference material being nonvolatile at the operating temperature, saidfirst tube being an oxide of the metal of said oxygen reference materialand acting as an electronicconductor at the operating temperature, athermocouple passing into said first tube and having leads connected toits inner-end, a lead wire electrically connected to said first tube, asecond tube surrounding said first tube and said button with its outerend in sealing engagement with said button, said leads and lead wirepassing through said second tube, a second electronic conductor adaptedto contact said fluid, and means connected to said lead wire and saidsecond electronic conductor to measure the voltage flow through saidfluid.

2. Apparatus according to claim 1 in which said first tube is made of(3,0,, said button is made of ZrO, containing 3 to l% CaO, saidreference material is of the class consisting of chromium and chromiumalloys, and said electronic conductor is a mixture of Al,0 andmolybdenum.

3. Apparatus according to claim 2 in which said second electronicconductor is a third tube surrounding said second tube.

4. Apparatus according to claim 3 including a molybdenum cap sealing theupper end of said first tube with said lead wire and thermocouplepassing therethrough.

5. Apparatus according to claim 4 including a flange extending radiallyoutward from the inner end of said second tube, a flange extendingradially outward from the inner end of said third tube and abutting theflange on said second tube, an internally threaded sleeve surroundingsaid flanges and having a flange engaging the flange on said third tube,a male threaded cap threaded into said sleeve, and a lead extendingbetween said cap and said voltage measuring means.

6. Apparatus according to claim 5 in which said internally threadedsleeve and male threaded cap are stainless steel.

7. Apparatus according to claim 6 including a protective sleevesurrounding a portion of said third tube with one end bearing againstthe flange of said stainless steel sleeve.

8. Apparatus according to claim 1 in which said second electronicconductor is a third tube surrounding said second tube.

9. Apparatus according to claim 8 including a protective sleevesurrounding said third tube on the inner sideof said first tube.

10. Apparatus according to claim 8 including a flange extending radiallyoutward from the inner end of said second tube, a flange extendingradially outward from the inner end of said third tube and abutting theflange on said second tube, an internally threaded sleeve surroundingsaid flanges and having a flange engaging the flange on said third tube,a male threaded cap threaded into said sleeve, and a lead extendingbetween said cap and said voltage measuring means.

11. Apparatus according to claim 1 in which said second electronicconductor is an elongated member spaced from said second tube. 7

12. Apparatus according to claim 1 including a cap sealing the upperend-of said first tube with said lead wire and thermocouple passingtherethrough.

2. Apparatus according to claim 1 in which said first tube is made ofCr2O3, said button is made of ZrO2 containing 3 to 10% CaO, saidreference material is of the class consisting of chromium and chromiumalloys, and said electronic conductor is a mixture of Al2O3 andmolybdenum.
 3. Apparatus according to claim 2 in which said secondelectronic conductor is a third tube surrounding said second tube. 4.Apparatus according to claim 3 including a molybdenum cap sealing theupper end of said first tube with said lead wire and thermocouplepassing therethrough.
 5. Apparatus according to claim 4 including aflange extending radially outward from the inner end oF said secondtube, a flange extending radially outward from the inner end of saidthird tube and abutting the flange on said second tube, an internallythreaded sleeve surrounding said flanges and having a flange engagingthe flange on said third tube, a male threaded cap threaded into saidsleeve, and a lead extending between said cap and said voltage measuringmeans.
 6. Apparatus according to claim 5 in which said internallythreaded sleeve and male threaded cap are stainless steel.
 7. Apparatusaccording to claim 6 including a protective sleeve surrounding a portionof said third tube with one end bearing against the flange of saidstainless steel sleeve.
 8. Apparatus according to claim 1 in which saidsecond electronic conductor is a third tube surrounding said secondtube.
 9. Apparatus according to claim 8 including a protective sleevesurrounding said third tube on the inner side of said first tube. 10.Apparatus according to claim 8 including a flange extending radiallyoutward from the inner end of said second tube, a flange extendingradially outward from the inner end of said third tube and abutting theflange on said second tube, an internally threaded sleeve surroundingsaid flanges and having a flange engaging the flange on said third tube,a male threaded cap threaded into said sleeve, and a lead extendingbetween said cap and said voltage measuring means.
 11. Apparatusaccording to claim 1 in which said second electronic conductor is anelongated member spaced from said second tube.
 12. Apparatus accordingto claim 1 including a cap sealing the upper end of said first tube withsaid lead wire and thermocouple passing therethrough.